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Kevin T. Foley and Sanjay K. Gupta

Object. Standard techniques for pedicle screw fixation of the lumbar spine involve open exposures and extensive muscle dissection. The purpose of this study was to report the initial clinical experience with a novel device for percutaneous posterior fixation of the lumbar spine.

Methods. An existing multiaxial lumbar pedicle screw system was modified to allow screws to be placed percutaneously by using an extension sleeve that permits remote manipulation of the polyaxial screw heads and remote engagement of the screw-locking mechanism. A unique rod-insertion device was developed that linked to the screw extension sleeves, allowing for a precut and -contoured rod to be placed through a small stab wound. Because the insertion device relies on the geometrical constraint of the rod pathway through the screw heads, minimal manipulation is required to place the rods in a standard submuscular position, there is essentially no muscle dissection, and the need for direct visual feedback is avoided. Twelve patients (six men and six women) who ranged in age from 23 to 68 years underwent pedicle screw fixation in which the rod-insertion device was used. Spondylolisthesis was present in 10 patients and osseous nonunion of a prior interbody fusion was present in two. All patients underwent successful percutaneous fixation. Ten patients underwent single-level fusions (six at L5—S1, three at L4–5, and one at L2–3), and two underwent two-level fusions (one from L3–5 and the other from L4—S1). The follow-up period ranged from 10 to 19 months (mean 13.8 months).

Conclusions. Although percutaneous lumbar pedicle screw placement has been described previously, longitudinal connector (rod or plate) insertion has been more problematic. The device used in this study allows for straightforward placement of lumbar pedicle screws and rods through percutaneous stab wounds. Paraspinous tissue trauma is minimized without compromising the quality of spinal fixation. Preliminary experience involving the use of this device has been promising.

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Denis J. DiAngelo and Kevin T. Foley


An experimental study was performed to determine the biomechanical end-mounting configurations that replicate in vivo physiological motion of the cervical spine in a multiple-level human cadaveric model. The vertebral motion response for the modified testing protocol was compared to in vivo motion data and traditional pure-moment testing methods.


Biomechanical tests were performed on fresh human cadaveric cervical spines (C2–T1) mounted in a programmable testing apparatus. Three different end-mounting conditions were studied: pinned–pinned, pinned–fixed, and translational/pinned–fixed. The motion response of the individual segmental vertebral rotations was statistically compared using one-way analysis of variance and Student-Newman-Keuls tests (p < 0.05 unless otherwise stated) to determine differences in the motion responses for different testing methods.


A translational/pinned–fixed mounting configuration induced a bending-moment distribution across the cervical spine, resulting in a motion response that closely matched the in vivo case. In contrast, application of pure-moment loading did not reproduce the physiological response and is less suitable for studying disc arthroplasty and nonfusion devices.

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Langston T. Holly and Kevin T. Foley

✓ The authors sought to evaluate the feasibility and accuracy of three-dimensional (3D) fluoroscopic guidance for percutaneous placement of thoracic and lumbar pedicle screws in three cadaveric specimens.

After attaching a percutaneous dynamic reference array to the surgical anatomy, an isocentric C-arm fluoroscope was used to obtain images of the region of interest. Light-emitting diodes attached to the C-arm unit were tracked using an electrooptical camera. The image data set was transferred to the image-guided workstation, which performed an automated registration. Using the workstation display, pedicle screw trajectories were planned. An image-guided drill guide was passed through a stab incision, and this was followed by sequential image-guided pedicle drilling, tapping, and screw placement. Pedicle screws of various diameters (range 4–6.5 mm) were placed in all pedicles greater than 4 mm in diameter. Postoperatively, thin-cut computerized tomography scans were obtained to determine the accuracy of screw placement.

Eighty-nine (94.7%) of 94 percutaneous screws were placed completely within the cortical pedicle margins, including all 30 lumbar screws (100%) and 59 (92%) of 64 thoracic screws. The mean diameter of all thoracic pedicles was 6 mm (range 2.9–11 mm); the mean diameter of the five pedicles in which wall violations occurred was 4.6 mm (range 4.1–6.3 mm). Two of the violations were less than 2 mm beyond the cortex; the others were between 2 and 3 mm.

Coupled with an image guidance system, 3D fluoroscopy allows highly accurate spinal navigation. Results of this study suggest that this technology will facilitate the application of minimally invasive techniques to the field of spine surgery.

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Paul Park and Kevin T. Foley

Minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) is a relatively new surgical procedure that appears to minimize iatrogenic soft tissue and muscle injury. The authors describe a technique for MI-TLIF that permits the surgeon to reduce spondylolisthesis percutaneously. The results in 40 consecutive patients who underwent MI-TLIF for symptomatic spondylolisthesis utilizing this approach are reviewed. Thirty cases involved a degenerative spondylolisthesis while the remaining 10 were isthmic. The minimum follow-up was 24 months with a mean of 35 months. The mean preoperative Oswestry Disability Index score was 55, decreasing to a mean of 16 postoperatively. The mean leg and back pain visual analog scale scores were 65 and 52, respectively, improving to means of 8 and 15. Reduction of the spondylolisthesis was achieved in all cases, with a mean decrease in forward translation of 76%. The authors conclude that MI-TLIF for symptomatic spondylolisthesis appears to be an effective surgical option with results that compare favorably to open procedures.

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Kevin T. Foley, Maurice M. Smith and Y. Raja Rampersaud

The purpose of this study was to determine the feasibility of performing far-lateral lumbar discectomy by using the microendoscopic discectomy (MED) technique. The authors studied 11 consecutive patients with unilateral, single-level radiculopathy secondary to far-lateral disc herniation. There were eight men and three women, with an average age of 43 years. In all patients magnetic resonance imaging and/or computerized tomography scanning documented far-lateral disc herniations. Six patients experienced motor deficits, nine patients sensory abnormalities, and five depressed reflexes. All patients complained of radicular pain, which failed to improve with conservative care.

After induction of epidural anesthesia, single-level, unilateral percutaneous discectomies were performed using the MED technique. Five discectomies were performed at L3-4 and six at L4-5. There were four contained and seven sequestered disc herniations. All surgeries were performed on an outpatient basis. Follow up ranged from for 12 to 27 months. Improvement was shown in all patients postoperatively. Using modified Macnab criteria to assess results of surgery, there were 10 excellent results and one good result. None of the patients experienced residual motor deficits, four had residual decreased sensation, and one still had some degree of nonradicular pain. There were no complications.

Although various open techniques exist for the treatment of far-lateral disc herniation, MED is unique in that far-lateral pathological entities can be directly visualized and removed via a 15-mm paramedian incision. The percutaneous approach avoids larger, potentially denervating and destabilizing procedures. The need for general anesthesia can be avoided, and surgery is performed on an outpatient basis, thereby reducing hospital cost and length of stay.

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Langsto T. HOLLY, Ulrich Batzdorf and Kevin T. Foley

Object. In this report the authors review their 5-year experience in the diagnosis and management of nine patients with severe retromastoid pain secondary to C1–2 arthrosis. Patients with symptomatic joints unresponsive to nonoperative therapy underwent cervical fusion procedures.

Methods. The mean age of the patients was 71 years, and the onset of prior symptoms ranged from 6 months to 18 years. All patients suffered similar discrete nonneuropathic pain without radicular symptoms ipsilateral to the diseased facet joint. Four patients experienced relief from pain with the use of nonoperative therapy. Five patients continued to experience intractable pain and underwent C1–2 fusion. The follow-up period ranged from 6 to 26 months. The cervical fusion procedure was successful in treating the retromastoid pain in all patients. In patients who underwent surgery, complete relief of pain was demonstrated in four and significantly reduced in the fifth.

Conclusions. The authors have drawn several conclusions. First, C1–2 arthrosis has a rather unique presentation and is a potential cause of upper posterior neck and head pain predominantly in elderly patients. Second, nonoperative management significantly improved the pain in nearly half of their patients and should be the first line of treatment. Last, C1–2 fusion was successful in treating the pain in patients in whom nonoperative management had failed to resolve symptoms.

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Kevin T. Foley, Leslie D. Cahan and Grant B. Hieshima

✓ A portable digital subtraction unit has been used in the operating room as an important improvement in obtaining high-quality intraoperative angiograms. This digital subtraction system offers several advantages over previously described techniques for intraoperative studies. Not only are the images of good quality, but also the dose of contrast medium is reduced and a real-time imaging capability allows the surgeon to visualize the passage of contrast agent dynamically. Arterial injections may be performed by selective femoral cerebral catheterization, puncture of the cervical carotid artery, retrograde catheterization via the superficial temporal artery, or puncture of an intracranial vessel at the time of surgery.

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Langston T. Holly, James D. Schwender, David P. Rouben and Kevin T. Foley

✓The authors provide an overview of the minimally invasive transforaminal lumbar interbody fusion (TLIF) procedure including indications, technique, and complications. This novel technique is a method of achieving circumferential lumbar fusion using a unilateral dorsal approach. Minimally invasive TLIF uses a tubular retractor that is inserted via a muscle-dilating exposure, thereby minimizing the approach-related morbidity. This procedure is ideal for refractory mechanical low-back and radicular pain associated with spondylolisthesis, degenerative disc disease, and recurrent disc herniation. The authors' clinical experience and review of the medical literature indicate that TLIF can be effectively and safely performed in a minimally invasive fashion.

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Regis W. Haid, Kevin T. Foley, Gerald E. Rodts and Bryan Barnes

The authors review historical and biomechanical aspects of anterior cervical plate (ACP) systems. They propose a novel classification system for ACPs based on the biomechanical and graft-loading properties of these systems.

A retrospective review of the literature comprising both clinical and laboratory investigations regarding the ACP system was undertaken. Comparison of each system is considered in the context of the biomechanical attributes and graft-loading properties of each type of plate. Salient characteristics reviewed include restriction of screw backout, screw-angle variability, and mobility at the screw–plate interface. A new classification system for ACPs is proposed that primarily considers the ability of the construct to restrict screw backout, as well as the properties of the plate–screw interface—that is, the capacity for rotational or translational movement.

A new classification system is presented that provides unified, biomechanically descriptive nomenclature. Using this nomenclature, the ACP devices currently available and those developed in the future can be uniformly categorized.